Jamie Dimon, chairman and chief executive of JP Morgan Chase, today dismissed stories about one of the bank’s derivative traders cornering the credit default swap market as a “tempest in a teapot”.

Reports in the Wall Street Journal and Bloomberg this month suggested that Bruno Iksil, a trader nicknamed the 'London whale' who works in the bank's UK chief investment office, had built up a huge position in credit default swaps that is distorting the market.